1. Field of the Invention
The present invention relates to a method for producing narrow wires comprising titanium oxide, and narrow wires and structures produced by the same method, in particular a method for producing titanium oxide whiskers. More particularly, the titanium oxide whisker is useful for a variety of areas as a functional material for electronic devices and microdevices, or as a structural material. More concretely, the whisker as a functional material is useful for, e.g., photoelectric transducers, photocatalytic devices and electron-emitting materials.
2. Related Background Art
Titanium oxide-based materials have been extensively studied to apply their photosemiconducting characteristics and photocatalytic functions to photovoltaic cells, decomposition of toxic materials and antimicrobial purposes.
For example, Japanese Patent Application Laid-Open No. 8-302498 discloses examples in which finely powdered titanium oxide is used as a construction material for its antimicrobial function.
M. Gratzel et al. made, on a trial basis, a wet type photovoltaic cell using microparticles of TiO.sub.2, several nm in size, prepared by spreading colloidal solution and heating (baking), which shows an energy conversion efficiency of 7.1 to 7.9% (B. O'Regan et al., "NATURE," 353 (1991) 737). This relatively high conversion efficiency is realized by decreasing size of titanium oxide particles to the order of nanometer to increase their surface area.
More recently, it is reported that titanium oxide comes to show a unique surface characteristics of being macroscopically hydrophilic and oleophilic when irradiated with ultraviolet ray, because of formation of hydrophilic and oleophilic regions, 30 to 80 nm in size, on the surface ("NATURE," 388 (1997) 431).
These phenomena suggest that titanium oxide potentially exhibits new functions, when its size is decreased to the order of nanometer. It is discussed that titanium oxide as an n-type semiconductor exhibits characteristic electrical, optical and chemical properties in containment of electrons and surface functions, when its size is decreased to a certain characteristic level. However, the mechanisms involved are largely left unknown.
Therefore, titanium oxide material is expected to have wide applications as a new functional material for, e.g., electronic devices and microdevices, and also as a structural material.